1. TREM Receptors
Innate immunity is crucial for host survival during the early stages of infection. However, fine-tuning of this response is absolutely crucial to prevent excessive inflammation and tissue damage (Ford J. W. & McVicar D. W. Curr Opin Immunol 2009; 21, 38-46). Pathogen sensing is achieved through a constellation of pathogen recognition receptors, such as the toll-like receptors (TLR), which activate innate immune cells to clear the pathogen and to shape the adaptive immune response. Other innate immune receptors, such as the triggering receptor expressed on myeloid cells (TREM), modulate the innate response either by amplifying or dampening TLR-induced signals, and thus play crucial roles in fine-tuning of the inflammatory response. Since the discovery of triggering receptor expressed on myeloid cells (TREM)-1 in 2000, evidence documenting the profound ability of the TREM and TREM-like receptors to regulate inflammation has rapidly accumulated (Bouchon et al. J Immunol 2000; 164:4991-5; Ford J. W. & McVicar D. W. Curr Opin Immunol 2009; 21, 38-46; Bouchon et al. Nature 2001; 410:1103-7; Gibot S. Crit Care 2005; 9:485-9; Gibot et al. J Exp Med 2004; 200:1419-26; Gibot et al. Shock 2009; 32:633-7; Gibot et al. Crit Care Med 2008; 36:504-10; Klesney-Tait et al. Nat Immunol 2006; 7:1266-73; Murakami et al. Arthritis Rheum 2009; 60:1615-23; Sharif O. & Knapp S. Immunobiology 2008; 213:701-13; Ling et al. Chinese Med J 2010; 123:1561-5). The TREM and TREM-like receptors are a structurally related protein family encoded by genes clustered on mouse chromosome 17C3 and human chromosome 6p21. The TREM cluster includes genes encoding TREM-1, TREM-2 and, in the mouse, TREM-3, as well as the ‘TREM-like’ genes. The ‘TREM-like’ genes Treml1 and Treml2 in mouse, and TREML1 and TREML2 in humans, encode TREM-like transcripts 1 and 2 (TLT-1 and TLT-2, respectively). Monocytes, macrophages, myeloid dendritic cells, plasmacytoid dendritic cells, neutrophils, microglia, osteoclasts, and platelets all express at least one member of the TREM family, underscoring the importance of these proteins in the regulation of innate resistance, are expressed on a variety of innate cells of the myeloid lineage including neutrophils, monocytes, macrophages, microglia, osteoclasts, and dendritic cells, as well as on megakaryocytes and platelets.
Recent work on the TREM family includes: characterization of a new receptor expressed on plasmacytoid dendritic cells; definition of a key role for TREM in sepsis, cancer, inflammatory bowel disease and multiple sclerosis; an expanded list of diseases associated with the release of soluble forms of TREM proteins; and identification of the first well characterized TREM ligand: B7-H3, a ligand for TLT-2. Moreover, analysis of TREM signaling has now identified key regulatory components and defined pathways that may be responsible for the complex functional interactions between the TREM and TLRs. Together these findings define the TREM receptors as pluripotent modifiers of disease through the integration of inflammatory signals with those associated with leukocyte adhesion.
2. TREM-Related Pathologies
2.1. Sepsis
Septicemia, an invasion of the bloodstream by virulent bacteria that multiply and discharge their toxic products, is the serious and sometimes fatal disorder, commonly known as blood poisoning. The invasive organisms are usually streptococci or staphylococci but may be any type of bacteria. Septicemia is an extremely dangerous disorder because it spreads rapidly throughout the body. If bacteria continue to multiply in the bloodstream and the condition progresses to septic shock, blood pressure plummets and organ systems begin to shut down. Septic shock is characterized by massive release of proinflammatory mediators and leads not only to tissue damage, but also to haemodynamic changes, multiple organ failure (multiple-organ dysfunction syndrome, MODS), and ultimately death. More than 750,000 cases of sepsis occur annually in the US, and 215,000 of those afflicted die even with intensive medical care that includes antibiotics, intravenous fluids, blood transfusions, kidney dialysis, nutritional and respiratory support and sometimes surgery to remove the source of an infection. The incidence of sepsis has nearly doubled in the last decade and is expected to rise further, as the population ages and more people survive with conditions that leave them vulnerable. Despite the use of potent antibiotics and advanced resuscitative equipment costing $17 billion a year, septic shock remains the most common cause of death in non-coronary intensive care units (ICUs). Despite advances in methods and compositions for treatment of sepsis (US Pat Appl 20090012025), activated protein C (Xigris, drotrecogin-alpha, marketed by Eli Lilly) is the only FDA-approved drug for sepsis. However, Xigris has a very limited use—only in patients with high risk of death. Xigris should only be administered in an ICU and has significantly less effective protection if delayed in practice. Also, its use is limited to non-surgical patients due to the adverse effects on coagulation. Thus, there is a great need for an effective novel treatment for sepsis.
Initial findings established TREM-1 as an amplifier of the systemic inflammatory response syndrome associated with sepsis. Blockade of TREM-1 has been shown to protect mice against lipopolysaccaride (LPS)-induced shock, as well as microbial sepsis caused by live Escherichia coli or caecal ligation and puncture (Bouchon et al. Nature 2001; 410, 1103-7). These results demonstrate a critical function of TREM-1 in acute inflammatory responses to bacteria and implicate TREM-1 as a promising therapeutic target for sepsis.
2.2. Acute Mesenteric Ischemia
Acute mesenteric ischemia is an abdominal emergency associated with 60 to 90% mortality (Lock G. Best Pract Res Clin Gastroenterol 2001; 15:83-98; Gibot et al. Crit Care Med 2008; 36:504-10). Although ischemia by itself induces little damage, reperfusion of the previously ischemic organ can yield to remote organ injury and life-threatening multiple organ failure. Even though numerous modalities and substances have been studied to reduce gut ischemia/reperfusion (I/R)-induced mortality, none have been entirely successful. As such, the development of effective strategies for preventing and treating circulatory collapse and organ injury after gut I/R is critical for the improvement of patient outcome under such conditions.
Recently, inhibition of TREM-1 has been shown to prevent an I/R-induced marked increase in ileal mucosal permeability and an associated bacterial translocation and to delay mortality (Gibot et al. Crit Care Med 2008; 36:504-10), indicating that the inhibition of the TREM-1 pathway may be useful during acute mesenteric ischemia.
2.3. Hemorrhagic Shock
Hemorrhagic shock is a condition of reduced tissue perfusion, resulting in the inadequate delivery of oxygen and nutrients that are necessary for cellular function. Whenever cellular oxygen demand outweighs supply, both the cell and the organism are in a state of shock. Hemorrhagic shock is primarily caused by traumatic injury, from automobile accidents, bullet or knife wounds, and falls. Trauma causes approximately 150,000 deaths per year, and is the leading cause of death in the population under age 45 in the United States. The resulting loss of productive life years exceeds that of any other disease, with estimated societal costs of >$450 billion annually. Most trauma deaths result from insufficient tissue perfusion due to excessive blood loss. Clinical management of hemorrhagic shock relies on massive and rapid infusion of fluids to maintain blood pressure. However, the majority of victims with severe blood loss do not respond well to fluid restoration. The development of effective strategies for resuscitation of traumatic blood loss, therefore, is urgently needed.
Recently, it has been shown that early inhibition of the TREM-1 pathway may be useful during severe hemorrhagic shock in rats in preventing organ dysfunction and improving survival (Gibot et al. Shock 2009; 32:633-7).
2.4. Rheumatoid Arthritis and Other Rheumatic Diseases
Rheumatic diseases are characterized by inflammation (signs are redness and/or heat, swelling, and pain) and loss of function of one or more connecting or supporting structures of the body. They especially affect joints, tendons, ligaments, bones, and muscles. Common symptoms are pain, swelling, and stiffness. Some rheumatic diseases can also involve internal organs. There are more than 100 rheumatic diseases including but not limiting to arthritis, ankylosing spondylitis, fibromyalgia, lupus, scleroderma, polymyositis, dermatomyositis, polymyalgia rheumatica, bursitis, tendinitis, vasculitis, carpal tunnel syndrome, complex regional pain syndrome, juvenile arthritis, Lyme disease, systemic lupus erythematosus, Kawasaki disease, fibromyalgia, and chronic fatigue syndrome. Rheumatic diseases may cause pain, stiffness, and swelling in the joints and other supporting body structures, such as muscles, tendons, ligaments, and bones. However, rheumatic diseases can affect other areas of the body, including internal organs. Some rheumatic diseases involve connective tissues (called connective tissue diseases), while others may be caused by autoimmune disorders, which are diseases involving the body's immune system attacking its own healthy cells and tissues. Rheumatic diseases are the leading cause of disability among persons age 65 and older. According to the Centers for Disease Control and Prevention, as of 2002, more than 70 million people in the U.S. have some form of arthritis (one in every three adults). This includes roughly 300,000 children that suffer from some form of arthritis or rheumatic disease, and millions more are at risk of developing one of these diseases. Most persons over the age of 75 are affected with osteoarthritis (also called degenerative joint disease) in at least one joint, making this condition a leading cause of disability in the US. Rheumatoid arthritis (RA) is an autoimmune disease characterized by synovial hyperplasia with massive infiltration of inflammatory cells, which leads to degeneration of cartilage, erosion of bone, and ultimately loss of function in the affected joints. Rheumatoid arthritis is the most crippling form of arthritis and affects approximately 2.1 million Americans and two to three times more women than men. Further, the average onset for rheumatoid arthritis is between the ages of 20 and 45 years old. Currently, arthritis disables 19 million Americans and takes a $128 billion toll annually on the U.S. economy in direct and indirect medical costs.
Recently, blockade of TREM-1 has been shown to represent a new promising approach to rheumatic diseases that is safer than the presently available immunosuppressive treatments (Murakami et al. Arthritis Rheum 2009; 60:1615-23).
2.5. Non-Small Cell Lung Cancer
Non-small cell lung cancer (NSCLC) accounts for about 87% of all lung cancer patients and affects more than 1.2 million people a year with around 1.1 million deaths annually in the US and worldwide. Estimated new cases and deaths from lung cancer (non-small cell and small cell combined) in the United States in 2010 are 222,520 and 157,300, respectively. Despite advances made in cytotoxic chemotherapy, NSCLC still kills more patients than breast, colon and prostate cancer taken together. Thus, there is a great need for an effective novel treatment for NSCLC. However, although lung cancer, and particularly primary NSCLC, is the leading cause of malignancy-related mortality in the United States, the biology of this devastating disease is complex and poorly understood.
Recent findings established that TREM-1 and the inflammatory response play an important role in cancer progression. It has been shown that cancer cells can directly up-regulate TREM-1 expression in patients' macrophages and that TREM-1 expression in tumor-associated macrophages is associated with cancer recurrence and poor survival of patients with NSCLC (Ho et al. Am J Respir Crit Care Med 2008; 177:763-70). These results demonstrate a critical function of TREM-1 in cancer progression and implicate TREM-1 as a promising target for the development of new rational anticancer therapy. It can be expected that blocking activation of the TREM-1 pathway may significantly improve survival of patients with NSCLC.
3. Current Approaches to Inhibit the TREM-1 Pathway
Antibodies have been considered as clinically significant therapeutic agents for various TREM-related pathologies (US Pat Appl 20080247955; Piccio et al. Eur J Immunol 2007; 37:1290-301). However, antibody therapy poses serious disadvantages. First, as antibodies are natural products they must be produced in cell lines or other live expression systems. This raises a question that there could be contamination of antibody preparations by infectious agents such as prions or viruses. Although tight regulation and regulatory vigilance and surveillance can reduce this concern, the need for ongoing monitoring and testing for contamination contributes to the high cost of developing and administering antibody therapies. In addition, antibody-based therapies require considerable logistical support. As antibodies are proteins, they cannot be given orally, except for those used to treat certain types of mucosal infectious diseases, and therefore, systemic administration is required. Another serious disadvantage of antibody-based therapies is the high costs of production, storage, and administration. Moreover, long infusions (i.e., for example, an hour or longer) require a hospital environment and are often associated with mild to very severe side effects. For example, in one trial, in which four patients in the U.K. were given an anticancer antibody reactive against an important receptor on T cells (CD28) severe and life-threatening responses were observed; the cause is at present not understood. This makes large-scale clinical applications of a number of monoclonal antibodies with demonstrated therapeutic activity impossible or, at least, severely compromised. Fast degradation of the administered antibodies is another drawback of antibody-based therapy.
As described in US Pat Appls 20090081199 and 20030165875, fusion proteins between human IgG1 constant region and the extracellular domain of mouse TREM-1 or that of human TREM-1 can be used, as a “decoy” receptor, to inhibit TREM-1. However, these large protein molecules have poses serious disadvantages similar to those of antibodies.
U.S. Pat. No. 6,420,526 entitled “186 Secreted Proteins” claims unspecified and unexemplified isolated fragments of TREM-1 containing at least 30 contiguous amino acids of human TREM-1. No biological data relating to such fragments are provided.
Peptides based on TREM-1-derived sequences for disrupting TREM-1 function presumably by blocking binding of the receptor with its cognate ligand have also been disclosed (US Pat Appl 20060246082) or published (Murakami et al. Arthritis Rheum 2009; 60:1615-23; Gibot et al. Crit Care Med 2008; 36:504-10; Gibot et al. Shock 2009; 32:633-7). Despite multiple advantages of these peptides as compared to antibodies, they have relatively low efficacy in terms of inhibiting TREM-1, thus having a high potential for toxicity and side effects. For example, the systemic administration of a synthetic TREM-1 peptide that mimics short highly interspecies-conserved extracellular domains of TREM-1 and is often called as LP-17 suppresses collagen-induced arthritis, although the effect is not as complete as that observed following viral gene transfer (Murakami et al. Arthritis Rheum 2009; 60:1615-23).
What is needed is a broad-based TREM-targeted therapy designed to disrupt protein-protein interactions that may be administered to treat various TREM-related pathologies safely and effectively. It is therefore the object of the present invention to provide therapeutic compounds that can be used to treat various TREM-related disorders.